The invention refers to an internal-combustion engine with an exhaust gas turbocharger, optionally with a charge cooler, as well as a an exhaust gas recycling valve which is arranged within a connecting pipe, whereby the connecting pipe branches, in the direction of the flow, from the exhaust pipe before the exhaust gas turbine and enters into the charge pipe after the exhaust gas turbine.
In order to fulfill the expected strict legal regulations concerning emissions of nitrogen oxides, the developers and producers of diesel engines in commercial vehicles will be forced in the further to drastically reduce the emissions of nitrogen oxides produced by such engines.
In the test methods legally prescribed for diesel engines for commercial vehicles (Europe 13 stage test; USA Heavy Duty Transient Cycle) approx. 70 to 80% of the nitrogen oxides are produced at high engine loads. Up to the present day it was deemed impossible to apply recycling of exhaust gases at high engine loads, even though successfully used at low engine loads, to reduce emissions of nitrogen oxides, because, on the one hand, a strong increase of particle and soot emissions were to be expected, and, on the other hand, durability would be deceased by increased wear and tear. The increase in wear and tear occurs due to the fact that when uncleaned diesel exhaust gases are used, solid particles are dragged into the motor oil via the oil film on the cylinder walls. Furthermore, it was expected that by the recycling of exhaust gases, the charge temperature in the heavy-duty points would strongly be increased, which would promote the production of nitrogen oxides in the combustion, thus strongly impeding the decrease of nitrogen oxides by the recycling of exhaust gases.
A majority of present engines in commercial vehicles comprise, as stated above, a charge cooler for lowering production of nitrogen oxides, and reducing fuel consumption. A recycling of exhaust gases at high engine loads wold only make sense if the recycled exhaust gas would be added to the intake air stream before the charge cooler. This procedure is not feasible due to the fact that for achieving sufficient cooling unacceptable constructional efforts and excessive amounts of energy would be needed. Furthermore, particles contained in the recycled exhaust gases from conventional combustion engines would lead to soiling because of depositing and, consequently, ineffectiveness and blocking of the charge cooler.
Therefore the only remaining option would consist of cleaning the recycled gas or adding it to the intake air stream uncleaned--thus accepting the soiling--and heating the charge after the charge cooler.
It is also known, for the purpose of cooling the cylinder heat and the piston of high-performance engines, in particular racing engines, to inject water into the combustion chamber. It was noticed, as a side effect, that a reduction in the emissions of nitrogen oxides occurred.